Studies proposed in this project have two main objectives. One is to identify the rate-limiting reactions (regulatory sites) for cholesterol biosynthesis in brain and to determine how these reactions are affected by exogenous and endogenous changes accompanying normal brain maturation and impaired brain development. The second is to ascertain the role of cholesterol ester metabolizing enzymes in the pathogenesis of the central nervous system in demyelinating diseases. Experiments will be carried out to measure the relative rates of individual reactions within the multi-enzyme system for the biosynthesis of cholesterol from mevalonate. We will measure these rates at various stages of normal brain development and in impaired brain development, which occurs in myelin deficient mutant Jimpy, Jimpy MSD and Quaking mouse brain. We will study the properties of the cholesterol esterifying enzymes and the ester hydrolases in rat mouse and human brain and in human cerebrospinal fluid (CSF). In these experiments we will determine if the enzymes in CSF are derived from brain and if the activities of these enzymes in CSF and/or in brain tissue change in demyelinating conditions, and that the properties of enzymes in human brain resemble the enzymes in rat and mouse brain.